My boss, who's 56, does trail ultra-marathons. He was one of the six finishers in the inaugural Leadville 100 in 1983, and told me about two years ago that he's done over 300 races that were "longer than marathons". I think that's how HE defines ultra-marathon. Just this year, he did a 100K (the Zion 100 in Utah), a 50-miler, and a 100 (The Tahoe Rim 100). Those are just the ones I know of. He might have done more.... I know he did several really long (40+ mile) training runs as well.
The shortest RACE that's an ultra that I can think of is a 5oK. I can see how someone in a 100 mile race might say that a 50K isn't REALLY an ultra, but it clearly is, by definition. If a 50K isn't, then people running the Badwater might turn up their noses at 100s and make the same argument! I did a 25K trail race in May (my longest race so far, but not my longest run). They have a 50K version on the same course, and I'm kicking around the idea of trying that next year. If I do, and if I finish it, I will CERTAINLY consider it an ultra!
The shortest RACE that's an ultra that I can think of is a 5oK. I can see how someone in a 100 mile race might say that a 50K isn't REALLY an ultra, but it clearly is, by definition. If a 50K isn't, then people running the Badwater might turn up their noses at 100s and make the same argument! I did a 25K trail race in May (my longest race so far, but not my longest run). They have a 50K version on the same course, and I'm kicking around the idea of trying that next year. If I do, and if I finish it, I will CERTAINLY consider it an ultra!